Radio power consumption dominates power consumption in battery-operated wireless sensor network device. Thus, to ensure a long life of a wireless sensor network, sensor devices should communicate with each other while minimizing the use of their transceivers (radios). Most sensor network devices minimize the radio power consumption by, in the Media Access Control (MAC) layer, duty-cycling of radio listening. In duty-cycled radio listening, the radio is periodically wakened for a short time interval to receive packets, rather than the radio being left on continuously listening for transmissions targeting that device. Such duty cycling of the radios in a battery-operated sensor network greatly reduces the power consumption.
However, a problem of such low power duty-cycled MAC protocols is the latency in delivering packets. Since a receiver node periodically turns on its radio for short time durations to receive packets, a transmitter node may desire to postpone its transmission to the next wake-up time of the receiver, which can cause the delay of transmissions to increase by the wake-up period of the receivers. This problem becomes worse when duty-cycled MAC protocols are deployed in multihop wireless sensor networks. Since every intermediate node in the multihop delivery path needs to wait and then forward, in the worst case, delivering packet from a leaf source node to the sink node can be delayed by n-times the wake up period of duty-cycled MAC for each hop, where “n” is the number of hops.
Time Division Multiple Access (TDMA)-based duty cycling is one of the periodic listening techniques used in low power sensor network MAC protocols. In TDMA-based low power MAC protocols such as TSCH [IEEE 802.15.4e Low rate Wireless Personal Area Networks. Amendment 5: Amendment to the MAC sublayer. 2011] and wireless HART, a set of timeslots comprises a superframe. Specific timeslots in the superframe are assigned for the devices to allow them to exchange packets. The devices turn on their radios only at the assigned timeslot for packet transmission and reception.
Thus the duty-cycled TDMA network can control the timeslot of each node in multihop wireless sensor network to meet the requirements of multihop networks such as duty-cycle and latency. To minimize the latency of multihop wireless sensor network while maintaining the low active duration of network, a set of algorithms have been proposed in literature such as Green-wave algorithm [S. Guha, C.-K. Chau, and P. Basu, “Green wave: Latency and capacity efficient sleep scheduling for wireless networks,” in Proc. IEEE INFOCOM, March 2010], in which timeslots are assigned such that the wakeup timeslot of a node happens just before the wakeup timeslot of next hop in the multihop delivery path. However, some of the existing algorithms require a lot of detailed information on multihop network topology such as hop count of a node, neighbors of each node and a series of nodes in each multihop delivery path, which is not desirable for resource limited sensor network devices.